Project 1. Targeted Radiotherapy of Brain Tumors Using Modular Recombinant Transporters (RT) Labeled with Auger-Electron Emitting Radionuclides. Michael R. Zalutsky, Ph.D., Project Leader The long-term objective of this project is to develop more specific and effective targeted radiotherapeutics for brain tumor treatment that are based on a novel radionuclide delivery system that ultimately might be adaptable to the molecular signature of an individual tumor. This will be pursued by combining the expertise of the Duke University team in targeted radiotherapy with the innovative approaches pioneered at the Institute of Gene Biology, Russian Academy of Sciences, in modular recombinant transporters (MRT). MRT are engineered molecules that have been devised with domains that retain receptor binding, endosomal escape and nuclear translocation, thereby facilitating the delivery of drugs from the cell surface to the nucleus. We hypothesize that MRT targeted to the epidermal growth factor receptor (EGFR) might be an ideal vehicle for exploiting the high potency and sub-cellular range of Auger electrons for targeted radiotherapy. Auger electrons have low cytotoxicity when decaying outside the cell nucleus, i.e. on the cell surface or in the extracellular space. For this reason, Auger electron emitting MRT might be well suited to convection enhanced delivery because their sub-cellular range of action should minimize radiation dose to normal brain tissue, where decays occur outside the cell. Specifically, we propose to: 1) adapt labeling strategies already developed for labeling internalizing mAbs to optimize the attachment of Auger electron emitters to MRT;2) evaluate the cytotoxicity of radiolabeled EGF-MRT against EGFR-expressing human glioma cells in both monolayer and spheroid geometry;3) determine the tissue distribution and calculated radiation dosimetry of radiolabeled EGF-MRT in normal and tumor bearing mice;4) evaluate the maximum tolerated dose and therapeutic efficacy of radiolabeled EGF-MRT in subcutaneous and neoplastic meningitis rodent xenograft models;and 5) evaluate the therapeutic potential of Auger electron labeled EGF-MRT administered by intracerebral microinfusion to athymic rats with intracerebral human glioma xenografts. RELEVANCE (See instructions): Our goal is to develop more specific and effective treatments for brain tumors based on a modular recombinant transporter (MRT) designed to bind to epidermal growth factor receptors that are present in high abundance on glioma and then deliver a radioactive cargo to the nucleus of these cells. Labeling these MRT with Auger electron emitters, which only are highly cytotoxic when delivered to the cell nucleus, offers the exciting prospect of more tumor selective radiation therapy with less damage to normal tissue.